牢
láo · HSK 6
firm
🐄 Roof 宀 over cow 牛 — a cattle pen, built firm and sturdy
A pen that holds livestock must be solid. From cattle fold the meaning extends to firm, secure, and even prison (牢房). The sacrifice sense ties to penned animals raised for ritual.
牢 — roof 宀 + ox 牛
Originally a pictograph showing an ox (牛) penned under a roof or enclosure (宀), depicting a livestock pen or stable. From 'animal pen' it extended to mean 'prison' (a place of confinement) and then 'firm, secure, sturdy' — the sense of something solidly enclosed.